Shadow of the Colossus designer and unafraid-to-take-his-time auteur Fumito Ueda originally planned for the game to included 48 colossi. In the final game, there are only 16 of these huge, gentle monsters—which essentially mind their own business, roaming the game's lonely landscape until you take it upon yourself to kill them under seemingly divine mandate. (You can check it out in HD on the PS3 in the excellent Ico and Shadow Collection, which you should do if you haven't already.)
Now you can wonder how some Ueda's other colossi might have behaved. The link below has shots of several unused designs cut from the final game, which range from spindly spider-like creatures to mollusk-headed worms. None of them will make you any less sad over the lack of news for Ueda's The Last Guardian.